The present invention relates to technique for shift control of a continuously-variable transmission for a vehicle.
A Published Japanese Patent Application Publication (KOKAI) No. H04(1992)-54371 shows a continuously-variable transmission shift control system arranged to determine a target transmission ratio in accordance with a vehicle speed and an accelerator operation quantity by using a map of shift pattern. In this control system, however, if, during a normal running state with a relatively small accelerator operation quantity and a constant vehicle speed, a driver carries out a kickdown operation with the intention of rapid acceleration, the actual transmission ratio does not immediately reach a target ratio corresponding to the accelerator operation quantity. Consequently, the driving force does not increase immediately whereas the engine speed increases. During this, the engine falls into a state like racing, causing an unpleasant feeling to the driver.
A U.S. Pat. No. 4,764,155 (corresponding to JP2593432B2) discloses a continuously-variable transmission shift control system arranged to restrain a variation of a transmission ratio or hold the transmission ration constant when a driver's acceleration demand is great or when a throttle opening degree becomes greater than a threshold, in order to reduce a time delay from a throttle opening increase to attainment of the feel of acceleration.